Thomas Jefferson is quoted as saying: "Eternal vigilance is the price of liberty."

How true.

Americans must always remain vigilant. For opportunists of all stripes are constantly angling to snatch away freedom and liberty.

Neocons and warmongers aren't the only ones that perpetually try to keep Americans in a constant state of fear, with the solution always being a further sacrifice of life and liberty to the government. The other side of the spectrum is populated by the environmental prophets of doom.

Here are 18 examples of the spectacularly wrong predictions made around 1970 when "Earth Day" started:

1. Harvard biologist George Wald estimated that “civilization will end within 15 or 30 years unless immediate action is taken against problems facing mankind.”

2. “We are in an environmental crisis which threatens the survival of this nation, and of the world as a suitable place of human habitation,” wrote Washington University biologist Barry Commoner in the Earth Day issue of the scholarly journal Environment.

3. The day after the first Earth Day, the New York Times editorial page warned, “Man must stop pollution and conserve his resources, not merely to enhance existence but to save the race from intolerable deterioration and possible extinction.”

4. “Population will inevitably and completely outstrip whatever small increases in food supplies we make,” Paul Ehrlich confidently declared in the April 1970 Mademoiselle. “The death rate will increase until at least 100-200 million people per year will be starving to death during the next ten years.”

5. “Most of the people who are going to die in the greatest cataclysm in the history of man have already been born,” wrote Paul Ehrlich in a 1969 essay titled “Eco-Catastrophe! “By…[1975] some experts feel that food shortages will have escalated the present level of world hunger and starvation into famines of unbelievable proportions. Other experts, more optimistic, think the ultimate food-population collision will not occur until the decade of the 1980s.”

6. Ehrlich sketched out his most alarmist scenario for the 1970 Earth Day issue of The Progressive, assuring readers that between 1980 and 1989, some 4 billion people, including 65 million Americans, would perish in the “Great Die-Off.”

7. “It is already too late to avoid mass starvation,” declared Denis Hayes, the chief organizer for Earth Day, in the Spring 1970 issue of The Living Wilderness.

8. Peter Gunter, a North Texas State University professor, wrote in 1970, “Demographers agree almost unanimously on the following grim timetable: by 1975 widespread famines will begin in India; these will spread by 1990 to include all of India, Pakistan, China and the Near East, Africa. By the year 2000, or conceivably sooner, South and Central America will exist under famine conditions….By the year 2000, thirty years from now, the entire world, with the exception of Western Europe, North America, and Australia, will be in famine.”

9. In January 1970, Life reported, “Scientists have solid experimental and theoretical evidence to support…the following predictions: In a decade, urban dwellers will have to wear gas masks to survive air pollution…by 1985 air pollution will have reduced the amount of sunlight reaching earth by one half….”​10. Ecologist Kenneth Watt told Time that, “At the present rate of nitrogen buildup, it’s only a matter of time before light will be filtered out of the atmosphere and none of our land will be usable.”